Propeller blade



May 2 5, 1937. 'n -5QU|RE'$ A 2,081,647

' PBOPELLER BLADE Filed April 2, 1954 Z j FT, 5

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v INVENToR. v@7b/717 Squires.

ATTORNEYS.

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Patented May 25, 1937 UNITED l STATES PROPELLER BLADE John Squires, Hagerstown,

Md., assignor to United Aircraft Corporation, East Hartford, Conn., a corporation ofDelaware Original application July 5, 1933,

Serial No.

679,133.. Divided and this application April 2,

1934, Serial No. 718,574

5 Claims.

This invention relates to propeller blades and is a division of my application for Letters Patent of the United States iled on the 5th day of July, 1933, Serial No. 679,133, for improvements in Pro- 5 peller blade and method and apparatus for producing the same.

Objects of the invention include the provision of a propeller blade of hollow construction having a closed end or tip, such closed end or tip being provided with a vent opening therein; the provision of a propeller blade of hollow construction having a closed end or tip, such end or tip being provided with a relatively small opening in the suction face thereof for the purpose of venting the interior of the blade to the atmosphere; the provision of a hollow steel propeller blade having an open end anda closed end or tip provided with a relatively small opening through the suction face thereof whereby condensation collecting within the interior of the blade will be ejected therefrom under centrifugal action produced by rotation of the propeller and by the differential of pressure between the interior and the exterior of the propeller blade during operation of the propeller of which the blade forms a part; and the provision of a propeller and blades in which these forces will cause a limited circulationl of air through the blades during operation of the propeller thereby tending to evaporate any condensation occurring in the blade and discharge it therefrom.

Other objects include the provision of a hollow steel propeller blade having its internal surfaces lprotected against oxidization by means of a de( posited coating of moisture resisting material the provision of a hollow steel propellerl blade having its internal surfaces protected by an electrolytically deposited coating of moisture resisting metal; the provision of a hollow metal propelqu ler blade having its interior surfaces protected against the effects of moistureby a coating of paint or like material; and the provision of a hollow steel propeller blade having its interior surfaces-protected against the effects of moisture '45 by coatings of electrolytically deposited metal and of paint or like material.

Further objects include the provision of a propeller blade of hollow construction having a balancing mass applied internally thereof; the provision of a hollow steel propeller blade provided internally with a balancing mass comprising material adhering thereto; and the provision of a hollow steel propeller blade having any internally applied balancing mass comprising paint, enamel or the like.

The above being among the objects of the present invention, the same consists in certain features of construction and combinations of parts to 60 be hereinafter described with reference to the accompanying drawing, and then claimed, having the above and other objects in View.

In the accompanying drawing which illustrates a suitable embodiment'of the present invention and in which like numerals refer to like parts throughout the'several vdifferent views,

Figure l is a more or less diagrammatic front elevational view of an airplane propeller. l

Fig. 2. is an enlarged, partially broken, partially sectioned side elevational view of one of the blades of the propeller shown in Fig. 1.

Fig. 3 is an enlarged, transverse sectional view of the blade shown in Fig. 2, taken on the line 3-3 of Fig. 2.

Fig. 4 is a still further enlarged transverse sectional view taken on the line 4-4 of Fig. 2.

Fig. 5 is a reduced fragmentary sectional viewof the extreme tip portion of the propeller blade shown in Fig. 2, taken as on the line 5-5 of Fig. 4.

As is well understood in the art, hollow metal propeller blades, and particularly hollow steel propeller blades, oifer considerable advantages from the standpoint of strength and lightness over other types of propeller blades. One disadvantage of hollow steel propeller blades in the past has been that due to the changes in temperature to which the blades are subjected during operation on an airplane, and because of other reasons, moisture from the air within the blade condenses upon the inner walls thereof and not only fosters deterioration of the blade through rust or oxidization but in some cases may aiect the proper dynamic balance of the propeller as a whole due t'o unusual amounts of moisture condensing and becoming trapped in one of the blades. The/present invention has for its principal object the elimination of the effects of condensation-on the interior of such a blade as well as tl'e elimination of the condensate itself.

Referring to the-drawing and particularly Fig. l, an airplane propeller is shown as including a hub I0 provided with a pair of oppositely extending blade'socket portions I2 in each of which is suitably received and secured a propeller blade I4. As indicated in Figs. 2 to 5, inclusive, it will be noted that the blade I4 is of hollow construction and is provided at its shank end with a peripheral annular flange IIS provided for theepurpose of enabling the blade I4 to be secured in its corresponding socket of the hub I0, although it will be understood that, as far as the present invention is concerned, any suitable or conventional construction may be provided between the blade and the blade socket of the hub.

The opposite or tip end I8 of the blade I4 is closed, except as will hereinafter be described, and the wall thickness of the blade preferably decreases gradually from adjacent the flange I6 toward the tip I8 with the possible exception that the wall thickness of the extreme tip portion of the blade for manufacturing reasons is preferably thickened a slight amount as indicated in Fig. 5. It will also be understood that the blade I4 is of airfoil cross section, as indicated in Figs. 3 and 4, and with the thickness of the section decreasing toward the tip I8 of the blade.

The blade I4 is constructed of metal and, while any metal may be employed in the broader aspects of the present invention, the invention is particularly applicable to blades formed from steel due to the fact that condensation of moisture within steel blades usually presents a problem more diiiicult to overcome than in connection With hollow blades formed from metal not so readily subject to oxidization.

In preparing the blade I4 against the action of moisture therein, a small opening 20, which may be as small as zf of an inch, is drilled through the Wall of the blade adjacent the tip I8 thereof. The opening 20 is preferably provided in the forward or suction face of the blade for reasons which will hereinafter be morefully explained.

- The next step is tothoroughly clean the inner wall surfaces of the blade. The blade is then preferably placed in a plating bath and given a light coating 2I of suitable moisture resistingv metal such as copper, nickel or cadmium. which is applied to both inside and outside for the purpose of rendering it rust proof. Only a very light coating of such metal is necessary for, this purpose and a coating of cadmium .0003 of an inch thick has been found suflcient. After the blade has been cadmium plated it is again thoroughly cleaned and the inside is then provided with a coat 22 of paint 'orA like material to further render it resistant to the corrosive effects of moisture. This paint or paint-like material is preferably one of an elastic type such as elastic primers commonly found on the market. It will, of

course, be understood that the thicknesses of the coatings 2| and 22 are shown exaggerated in the accompanying drawing.

After the blade has thus been treated it is mounted in a balancing apparatus which may be of the type illustrated and described in the above referred to patent application of which the present application is a division, and there brought to a condition of minute accurate final balance and into conformance Witha predetermined standard balance. This is accomplished by the introduction of the required amount of paint or like material, preferably of the type above described, into the interior of the blade through the opening 20 in the tip of the blade. The paint thus introduced for balancing purposes may accumulate in the tip of the blade as indicated at 24 in Fig. 5, thus providing a balancing mass f or the blade located internally thereof and at the.

tip end thereof.

As will be apparent, by the use of paint interiorly applied, an extremely accurate condition of the final balance may be obtained and one that accurately conforms toV a predetermined standard of balance. From the above it will be apparent that the interior surface of the metal forming the blade I4 is doubly protected against contact with any moisture that maycondense onto the interior walls of the blade, first by the coating of cadmium the steel body of the blade and foster early destruction of the same. The vent opening 20 is provided for eliminating the accumulation of condensate within the interior of the blade for as the blade rotates with the propeller during operation any condensate which may be present within the interior of the blade is moved under the force of the centrifugal action of the turning propeller toward the tip end of the blade Where it may escapo through the opening 20.

Additionally, the opening 20 being in the front or suction face of the blade and the air within the bladel being subjected to the centrifugal force of the rotating propeller which thus tends to drive it toward the tip of the blade, the resulting higher than atmospheric pressure on the inside of the blade and the lower than atmospheric pressure area around the opening 20 on the outside of the blade exerts an additional force tending to draw any condensate in the vicinity of the opention of the propeller of which it forms a part.

This constant circulation of air through the blade additionallytends to absorb any moisture which may have condensed upon the interior Walls of the blade and not previously ejected and thus carry such moisture out of the blade with -the air through the opening 20. Accordingly, it will be recognized that by the apparatus herein provided an improved product results which is eiliciently protected from the corrosive eiiect of moisture within the blade and one in which a condition of minute nal balance may be obtained in an easy and economical manner.

Formal changes may be made in the specific embodiment of the invention described without departing from the spirit or substance of the broad invention, the scope of which is commensurate with the appended claims.

I claim: f

1. A hollow metal propeller blade having its internal surfaces covered by a coating of electrolytically deposited metal and-of paint-like material. Y

2. A hollow steel propeller blade, a coating of cadmium covering the internal surfaces thereof, and a; coating of paint-like material covering said cadmium coating.

3. A hollow steel propeller blade having a normally closed end, a coating of moisture resistive metal covering the internal surfaces of said blade for the purpose of protecting said surfaces against the effects of moisture, and a coating of paintlike material over the first mentioned coating to enhance -said protection afforded thereby, said blade having a vent opening adjacent said end for permitting the escape o'f moisture vthere-- through from the interior of said blade.

4. A hollow propeller blade having a balancing mass of paint-like material applied to and dried upon the hollow interior thereof.

5. In combination, a hollow metal propeller blade and a mass of paint-like material applied to and hardened upon the inner surfaces thereof adjacent the tip thereof for the purpose of permanently modifying the balance of said blade.

JOHN SQUIRES. 

